Martin HPL Repair... Glue?

[Keith Somerville]

Hello chaps,

A customer brought this in today. Apparently it happened at a party and no one will own up to it. Friends, eh?!

Wondering if anyone's had a go at repairing this Formica before and what glue and method they used.

--Keith

[Mark Fogleman]

I have had one of these repairs and used a thin wood veneer backer glued with Titebond Melamine glue to the inside and knitted the jagged edge back together. Pressure to the patch from the inside was with curved cauls and short dowels (like go bars) and a few squeeze clamps to the top and bottom to close the cracks on the outside. That glue has a long working time and is made for this job. Then I used an HPL crack filler colored to match to fill in. It didn't look like new but definitely looked better and was strong. 

[Paul Breen]

Ouch!

Nothing will make a repair invisible with plastic laminate.I think the best you can hope for is to get the break lined up, wick super glue in it and then add a fabric backing. Laminate broken this way is difficult to push all of the ins and outs of the break back in line. Plastic laminate is made of paper thin layers of whatever the sub-straight is, overlaid with a paper thin sheet of melamine, in which you see the color or pattern. When it breaks like this, the layers can fracture leaving a very irregular, layered break as you can see in the picture. You may have to file or sand some of it away to get the surface flush again.

There is a product called Seamfil that may help disguise things a bit cosmetically but it will be obvious, possibly less so than glue alone.

http://www.kampelent.com/seamfil.php

Martin builds these guitars using 3M #PR60056 to glue the plastic laminate parts to wood. I looked at the data sheet for this stuff and it is a cyanoacrylate formulated for plastics and rubbers, it's medium viscosity. Looks like they also offer a low viscosity and gel formulas. I think any good CA would work though. Keep some Acetone on hand for clean up. It will dissolve the CA but will not attack the laminate.

I could go off on a rant about plastic laminate use in instruments but will only suffice it to say that those that have these instruments cross their bench will also be muttering strings of expletives and pulling their hair out.

[Greg Mirken]

It can help to get the edges lined up to use a sanding stick or file and undercut both edges of the crack. Then a backing reinforcement spanning the whole side provides strength to the repair. Birch hobby plywood is a good choice for that- you can get it to flex to conform to the side curvature and clamp with rare earth magnets.

There's nothing wrong with these guitars except that salesmen neglect to inform the customer that they are pretty much non-repairable. And even if they did most people wouldn't understand.

[Keith Somerville]

Thanks for your replies, chaps. I had to put this to one side for a bit while I worked on the owner's other guitar. What glue would you use to fix a support backing onto the inside? I've ordered in some worktop filler and it'll be interesting to see how well that covers up the join.

[Paul Breen]

Titebond will adhere to the sanded side of plastic laminate.

[Brian Stewart]

I did one of these a few years ago.  I used woven graphite cloth and epoxy on the inside.  Messy and difficult, but strong.  Probably overkill...